1. Field of the Invention
The present invention relates to an optical film, to be specific, to an optical film used for daylighting of a building such as a house.
2. Description of Related Art
Conventionally, it has been known to introduce sunlight into indoors to adjust environment, for example, brightness of indoors of a building, so-called daylighting (also called sunlight lighting and daylighting). However, recently, in view of reduction in environment burden, it is desired to introduce sunlight more efficiently into indoors to reduce use of artificial lighting during day.
Thus, various examinations are conducted to improve indoor brightness by introducing sunlight efficiently into indoors by attaching an optical member to, for example, a window: the optical member being capable of changing traveling direction of light based on optical behavior such as light refraction, diffraction, or reflection.
For such an optical member, for example, Japanese Unexamined Patent Publication No. 2000-268610 has proposed a transparent plastic plate in which a plurality of slits extending in horizontal directions are arranged at fixed intervals in vertical directions.
Such a plastic plate is placed, for example, at a window of a house and allows daylighting by reflecting and refracting sunlight entered from outdoors through the window.